The use of polyorganosiloxanes in sealant compositions brings in many advantages like high temperature stability, UV resistance, oxidation resistance etc, but such sealant compositions suffer from very high gas permeability which make them less attractive. The gas permeability of polyorganosiloxane based sealants can potentially be reduced with the addition of inorganic fillers, achieving a balanced performance of reduced gas permeability with retention of processibility (viscosity control of the resultant composition). But maintaining suitable mechanical properties in such filled compositions still remains a challenging task.